This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-242866, filed Aug. 10, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a pulse generator, particularly relates to a pulse generator for generating a pulse train having a high repeat frequency and a high duty ratio.
2. Description of the Related Art
As is generally known, it is necessary for a pulse train which is used as a driving signal for a DEMUX apparatus, a short pulse light source and a super speed finder or the like, to have a high duty ratio having a high repeat frequency in the range from several GHz to 10 GHz with a narrow pulse width in the range from 10 ps (pico second) to 15 ps (not less than 60 GHz in frequency), for example.
Under a contemporary level of technology, the highest frequency capable of being stably oscillated by an oscillator which is configured by an electric circuit, is about 40 GHz.
Accordingly, it was not possible for one pulse generator to generate a pulse train having the high duty ratio having a high repeat frequency in the range from several GHz to 10 GHz with a narrow pulse width in the range from 10 ps to 15 ps.
Therefore, a pulse generator shown in FIG. 10A is recommended (Jpn. Pat. Appln. KOKAI Publication No. 2000-187190).
In other words, in the pulse generator shown in FIG. 10A, a sine wave generator 1 outputs a sine wave signal xe2x80x9caxe2x80x9d with a frequency fA in the range from several GHz to 10 GHz (a period Ta) as shown in FIG. 11A and transmits it to a half-wave rectifier 2.
This half wave rectifier 2 half-wave rectifies the inputted sine wave signal xe2x80x9caxe2x80x9d and transmits it to a next voltage amplifier 3 as a half-wave rectified signal b having a waveform as shown in FIG. 11B.
This voltage amplifier 3 amplifies the half-wave rectified signal b to output the half-wave rectified signal after being amplified, namely, a pulse train signal c as shown in FIG. 11C to an output terminal 4.
In the pulse generator which is configured in this manner, the pulse train signal c outputted from the output terminal 4 has a repeat frequency fA (repeat period Ta) as shown in FIG. 10B and can decrease pulse widths Tc of the respective pulses 5 composing this pulse train signal c to about xc2xd of the repeat period Ta.
Additionally, the pulse generator composed in this manner can decrease amount of a jitter generation of the respective pulses 5.
Further, other pulse generator shown in FIG. 12 is also recommended in the above document (Jpn. Pat. Appln. KOKAI Publication No. 2000-187190).
In other words, in this pulse generator shown in FIG. 12, for example, the sine wave generator 1 outputs the sine wave signal xe2x80x9caxe2x80x9d with a frequency fA in the range from several GHz to 10 GHz (a period Ta) and transmits it to a voltage amplifier 3a having a movable operating point.
As shown in FIGS. 13A and 13B, upon amplifying the inputted sine wave signal xe2x80x9caxe2x80x9d, this voltage amplifier 3a having a movable operating point can arbitrarily set an operation point (bias point) with respect to the inputted sine wave signal xe2x80x9caxe2x80x9d by changing a signal value of a operation point control signal which is inputted from the outside.
In FIG. 13A, the operating point (bias point) is set at a position at 0V of the inputted sine wave signal xe2x80x9caxe2x80x9d.
In this case, the amplified sine wave signal becomes a normal sine wave signal waveform in which a component in a (xe2x88x92) side and a component in a (+) side are substantially symmetric.
However, in this pulse generator, as shown in FIG. 13B, the operating point of the sine wave signal xe2x80x9caxe2x80x9d is set with being moved to a negative side.
Accordingly, the sine wave signal amplified by this voltage amplifier 3a has a waveform shape, of which a portion of the (xe2x88x92) side component is clipped.
As a result, a signal waveform of the sine wave signal which is amplified by this voltage amplifier 3a approximates the signal waveform of the amplified half-wave rectified waveform signal c shown in FIG. 11B in the aforementioned pulse generator shown in FIG. 10A.
In the case that the amplitude value (Pxe2x88x92P) of the amplified signal is fixed, as described above, the amplified sine wave signal, namely, the respective pulses 5 of a pulse train signal c1 to be outputted to an output terminal 4 from the voltage amplifier 3a have a more sharp peak waveform.
Therefore, by using the voltage amplifier 3a having a movable operating point, it is possible to obtain the pulse train signal c1 having a high duty ratio with a high repeat frequency in the range from several GHz to 10 GHz and a narrow pulse width under the state that the jitter generating amount is restrained.
However, even in the pulse generators of two types as shown in FIGS. 10A and 12A, there are problems to be solved as follows.
At first, as shown in FIGS. 11A, 11B, 11C, 13A and 13B, the pulse widths Tc of the respective pulses 5 composing the pulse train signals c and c1 to be outputted from these pulse generators are substantially determined in response to the repeat frequency Ta of the sine wave signal xe2x80x9caxe2x80x9d, so that this involves a problem that it is not possible to set the pulse widths Tc of the respective pulses 5 to an arbitrary value.
Further, the pulse widths Tc of the respective pulses 5 are limited to about xc2xd of the repeat period Ta of the sine wave signal xe2x80x9caxe2x80x9d, so that this involves a problem that it is not possible to obtain the high duty ratio in the pulse train signals c and c1.
Further, the pulse widths Tc of the respective pulses 5 in the pulse train signals c and c1 are limited to the frequency properties of the amplifiers 3 and 3a. 
In other words, in order to amplify the sine wave signal xe2x80x9caxe2x80x9d which is outputted from the sine wave generator 1, it is needed to have a higher frequency property than a frequency component of the frequency fA on this sine wave signal xe2x80x9caxe2x80x9d.
However, the highest frequency of the frequency properties of the amplifiers 3 and 3a are about 40 GHz similar to the sine wave generator 1.
Accordingly, for example, this involves a problem that it is not easy to obtain the extremely high duty ratio such that, for example, the pulse width of the pulse 5 is in the range from 10 ps to 15 ps or the like.
Additionally, the pulse train signals c and c1 which occur resulting from the difference of the frequency properties in the respective amplifiers 3 and 3a involve a problem that scattering occurs between the pulse generators each other.
The present invention has been made by taking the above problems into consideration, and it is an object of the present invention to provide a pulse generator of a simple structure capable of generating a pulse train having a high repeat frequency and a high duty ratio by making a pair of pulse trains, of which polarities are different each other, from one electric signal in a sine waveform and regulating the phase difference between these pulse trains each other.
(1) In order to attain the above object, the present invention provides a pulse generator comprising: signal generating means (11) for generating an electric signal in a sine waveform;
first pulse train generating means (12, 19, 22, 24) for generating a first pulse train having a positive polarity corresponding to the positive polarity element among a positive polarity element and a negative polarity element which configure the electric signal in the sine waveform outputted from the signal generating means;
second pulse train generating means (13, 20, 22, 23, 24) for generating a second pulse train having a negative polarity corresponding to the negative polarity element among a positive polarity element and a negative polarity element which configure the electric signal in the sine waveform outputted from the signal generating means;
phase difference setting means (14) for setting the phase difference between the first pulse train and the second pulse train so that a pulse of the first pulse train which is generated by the first pulse train generating means and a pulse of the second pulse train which is generated by the second pulse train generating means are partially superimposed temporally;
wave synthesizing means (15) for synthesizing the first pulse train and the second pulse train in which the phase difference is set by the phase difference setting means; and
half-wave rectifying means (16) for half-wave rectifying the output from the wave synthesizing means and generating a pulse train having a pulse width, narrower than any of the pulse widths owned by the first pulse train and the second pulse train.
(2) Further, in order to attain the above object, the present invention provides a pulse generator according to (1), wherein the first pulse train generating means includes a positive half-wave rectifying circuit for half-wave rectifying only a positive pole in a sine wave signal which is outputted from the signal generating means, and outputting a positive side rectified signal as the first pulse train; and
the second pulse train generating means includes a negative half-wave rectifying circuit for half-wave rectifying only a negative pole in a sine wave signal which is outputted from the signal generating means, and outputting a negative side rectified signal as the second pulse train.
(3) Additionally, in order to attain the above object, the present invention provides a pulse generator according to (2), wherein the phase difference setting means includes a delay circuit which is inserted in a rear stage of the negative half-wave rectifying circuit, and the delay circuit delays the negative side rectified signal which is outputted from the negative half-wave rectifying circuit by the delay time designated from the outside.
(4) Further, in order to attain the above object, the present invention provides a pulse generator according to (2), wherein the phase difference setting means includes a delay circuit which is inserted in a front stage of the negative half-wave rectifying circuit, and the delay circuit delays the sine wave signal which is outputted from the signal generating means by the delay time designated from the outside to provide it to the negative half-wave rectifying circuit for outputting a negative side rectified signal as the second pulse train.
(5) Further, in order to attain the above object, the present invention provides a pulse generator according to (1), wherein the first pulse train generating means includes a positive rectangular wave generating circuit for outputting a positive side rectangular wave signal as the first pulse train having a positive predetermined value only for a positive pole portion in a sine wave signal which is outputted from the signal generating means; and
the second pulse train generating means includes a negative rectangular wave generating circuit for outputting a negative side rectangular wave signal as the second pulse train having a positive predetermined value only for a negative pole portion in a sine wave signal which is outputted from the signal generating means.
(6) Additionally, in order to attain the above object, the present invention provides a pulse generator according to (5), wherein the phase difference setting means includes a delay circuit which is inserted in a rear stage of the negative rectangular wave generating circuit, and the delay circuit delays the negative side rectified signal which is outputted from the negative rectangular wave generating circuit by the delay time designated from the outside.
(7) Further, in order to attain the above object, the present invention provides a pulse generator according to (5), wherein the phase difference setting means includes a delay circuit which is inserted in a front stage of the negative rectangular wave generating an circuit, and the delay circuit delays the sine wave signal which is outputted from the signal generating means by the delay time designated from the outside to provide it to the negative rectangular wave generating circuit for outputting a negative side rectangular wave signal as the second pulse train.
(8) Further, in order to attain the above object, the present invention provides a pulse generator according to (1), wherein the first pulse train generating means includes a half-wave rectifying circuit for half-wave rectifying only a positive pole in the sine wave signal which is outputted from the signal generating means, and outputting a positive side rectified signal as the first pulse train; and
the second pulse train generating means includes a polarity reversing circuit for reversing a polarity of the positive side rectified signal which is outputted from the half-wave rectifying circuit, and outputting a negative side rectified signal as the second pulse train.
(9) Additionally, in order to attain the above object, the present invention provides a pulse generator according to (8), wherein the phase difference setting means includes a delay circuit which is inserted in a front stage of the polarity reversing circuit, and the delay circuit delays the positive side rectified signal which is outputted from the half-wave rectifying circuit by the delay time designated from the outside to provide it to the polarity reversing circuit for outputting a negative side rectified signal as the second pulse train.
(10) Further, in order to attain the above object, the present invention provides a pulse generator according to (1), wherein the first pulse train generating means includes a rectangular wave generating circuit for outputting a positive side rectangular wave signal as the first pulse train having a positive predetermined value only for a positive pole portion in the sine wave signal which is outputted from the signal generating means; and
the second pulse train generating means includes a polarity reversing circuit for reversing a polarity of the positive side rectangular wave signal which is outputted from the rectangular wave generating circuit, and outputting a negative side rectangular wave signal as the second pulse train.
(11) Further, in order to attain the above object, the present invention provides a pulse generator according to (10), wherein the phase difference setting means includes a delay circuit which is inserted in a front stage of the rectangular wave generating circuit, and the delay circuit delays the positive side rectangular wave signal which is outputted from the rectangular wave generating circuit, by the delay time designated from the outside to provide it to the polarity reversing circuit for outputting a negative side rectangular wave signal as the second pulse train.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.